President George W Bush said he looked forward to working with the Democratic-controlled Congress to implement the civilian nuclear deal, saying it marked "another step" in deepening ties with India, which he called "a vital world leader."

But Edward Markey, co-chairman of the House of Representatives Bipartisan Task Force on Non-proliferation, vowed that Congress would cast a careful eye on the fine print.

"I can only surmise that it includes provisions they fear will raise the hackles of Congress," said Markey.

"Of course the administration will argue that they aren't breaking the law, but I think that folks up on the (Capitol) Hill have become increasingly sceptical of the administration's legal arguments," he said.

Markey was among 23 House lawmakers who sent a letter to Bush this week reminding him that "any inconsistencies" between the agreement and US laws "will call congressional approval deeply into doubt."

Congress in December approved landmark legislation allowing US exports of civilian nuclear fuel and technology to India for the first time in 30 years, a move intended to reverse sanctions on the Asian giant for its nuclear tests.

But the new operating agreement goes one step further, allowing India to reprocess spent fuel under safeguards by the global nuclear watchdog, the International Atomic Energy Agency (IAEA), said US Undersecretary of State Nicholas Burns, the US pointman in the talks to frame the pact.

That right to reprocess spent US-sourced nuclear fuel has been given only to Japan and the European Union so far, and US lawmakers had expressed scepticism over safeguards needed to deter India from possibly diverting any nuclear material to its military weapons programme.

Burns said that India had to first establish a new national nuclear reprocessing facility under strict safeguards and then the two countries would agree on a set of arrangements and procedures for such activity.

India had given firm assurances that all nuclear material reprocessed would be used "only for peaceful purposes," Burns said.

Indian national security adviser MK Narayanan said the deal was not an opportunity for India to increase its nuclear arsenal.

Meanwhile, India's top nuclear scientist on Saturday hailed a nuclear pact with the United States as "a very good deal" that should satisfy both countries.

The long-delayed accord announced on Friday in Washington allows US exports of civilian nuclear fuel and technology to India for the first time in 30 years -- a move intended to reverse sanctions imposed on the Asian giant for its nuclear tests.

It also allows India to reprocess spent fuel under safeguards imposed by the International Atomic Energy Agency, going one step further than a law passed by the US Congress in December.